The present invention relates to a transfer material carrying control apparatus in an image generating device such as an electrophotographic copying machine, a printer, a facsimile terminal equipment, and so on, particularly in an image generating device of the system in which multiplex transfer is carried out to generate a color image, a composite image, and so on.
FIG. 6 is a configuration diagram illustrating an example of a color electrophotographic copying machine as an image generating device of the multiple transfer system, which is constituted by an automatic original document supply device 1, an image input portion 2, an image output portion 3, and a transfer material supply portion 4. A color original document is put on a platen glass 5 by the automatic original document supply device 1. The image input portion 2 is constituted by an imaging unit 6, a wire 7 for driving the unit, a driving pulley 9, and so on. By using a CCD line sensor and color filters in the imaging unit 6, in the case of full color of four colors, the image input portion 2 reads the color original document for each of B (blue), G (green) and R (red) colors which are primary colors of light.
After converting the read information into digital image signals, the image input portion 2 converts the reflective factor information into density information. After giving a variety of data processing onto the density information in order to improve the reproducibility of color, gradation, precision and so on, the image input portion 2 further converts the density information into picture element signals of Y (yellow), C (cyan), M (magenta) and K (black) which are primary colors of toner, decides the on-time of laser for every picture element in accordance with the picture element signals, and outputs the picture element signals and the on-time of the laser to the image output portion 3.
The image output portion 3 includes a scanner 10, a photosensitive drum 11 and so on, and the photosensitive drum 11 is surrounded by a charger 12 for electrifying the photosensitive drum 11 uniformly, a developing device 13 for developing an electrostatic latent image into a toner image, a transfer device 15 for transferring the toner image to a transfer material, and a cleaning device 16 for recovering residual toner having not been transferred. The photosensitive drum 11 is driven by an electric motor to rotate in the direction as shown in the illustrated arrow.
For example, a yellow image signal from the image input portion 2 is converted to a light signal in a laser output portion 10a of the scanner 10 to thereby generate a latent image corresponding to an original image, on the photosensitive drum 11 through a polygon mirror 10b, an f/.theta. lens 10c and a reflection lens 10d. If this yellow latent image is transferred to a transfer material after being developed, the photosensitive drum 11 is electrified by the charger 12 after residual toner is removed therefrom by the cleaner 16, and the laser output portion 10a outputs a cyan image signal. Thereafter, latent images of the respective image signals of the magenta and black are generated sequentially.
The developing device 13 includes a yellow developer 13Y, a cyan developer 13C, a magenta developer 13M and a black developer 13K, and the respective developers are provided around the rotation axis thereof. Development is performed by the yellow developer 13Y, which is positioned as illustrated, when a toner image of yellow as an example is generated, and the developing device 13 is rotated to move the cyan developer 13C to the position so as be in contact with the photosensitive drum 11 when a toner image of cyan is generated. Development of magenta and black is performed in the same manner as above.
The outer circumference of the transfer drum 15 constituting a transfer material holder is covered with a transfer material carrier constituted by a dielectric sheet, and the transfer drum 15 is coupled with a special electric motor or the photosensitive drum 11 through gears so as to be driven to rotate in the direction as shown by the illustrated arrow. The transfer drum 15 is surrounded by a transfer charger 17, toner charge controlling dischargers 19, a separation claw 20, dischargers 21, a cleaner 22, an absorbing opposite roll 23, and an absorbing charger 25. A transfer material is carried from the transfer material supply portion 4 to the transfer drum 15 through a subsidiary carrying roll 32 and a main carrying roll 31 constituting a transfer material carrying device 14, and absorbed into the dielectric sheet by corona discharge of the absorbing charger 25. The transfer drum 15 is rotated synchronously with the photosensitive drum 11, thereby transferring a toner image, developed with yellow as an example, to a transfer material by the transfer charger 17, and further transferring the other colors by the rotation of the transfer drum 15 sequentially.
After the transfer drum 15 rotates four times so that transferring of four colors is completed, the transfer material is discharged by the separating dischargers 19 provided inside and outside the transfer drum 15, separated by the separation claw 20, and carried to a fixer 29 by a carrying belt 27, and the toner image is fused and fixed by a heating and pressing roller 30. A copy cycle is thus completed.
In the above-mentioned transfer material carrying device 14, on/off timing of a clutch for driving the carrying rolls 31 and 32 is decided to absorb a transfer material into a dielectric sheet of the transfer drum 15 in order to surely carry the transfer material at predetermined timing. In such a case, there is a problem that if the transfer material is lagged in the carrying direction, the feeding the transfer material toward the absorbing surface of the photosensitive body is so unstable as to produce a clearance between the absorbing surface of the photosensitive body and the transfer material to thereby produce a transfer fault.
In order to solve this problem, as disclosed in Japanese Patent Post-Examination Publication No. Sho-60-27979, the subsidiary carrying roll 32 is driven before the main carrying roll 31 is driven so that a transfer material is bent to generate a loop, and the main carrying roll 31 is driven to align the leading edge of the transfer material if the quantity of this loop is normal, while the transfer material is discharged outside through another course if the quantity of the loop is not normal.
In the above-mentioned conventional system, however, the time from supplying a reference signal till transferring is predetermined in the case where control on the main carrying roll 31 is carried out on the basis of the reference signal obtained on the rotation position of the transfer drum. On the other hand, in delivering products or exchanging parts, the leading edge of a transfer material can reach a predetermined transfer point at different timings. Accordingly, even if read registration, that is, the main carrying roll 31 is operated it is necessary to adjust the above-mentioned read registration by changing the timing to start the operation of the main carrying roll 31.
This will be described with reference to FIG. 5. On the assumption that the initial value of the timing to start the operation of the subsidiary carrying roll 32 is T.sub.1, and the initial value of the timing to start the operation of the main carrying roll 31 is T.sub.3, setting is made so that a clutch for the subsidiary carrying roll is turned off after time T.sub.L which is taken for generation, of the optimum loop quantity, after a transfer material detecting sensor for detecting the fact that a transfer material has reached the position of the main carrying roll 31 is turned on at T.sub.2, and thereafter a clutch for the main carrying roll is turned on. If the main carrying roll 31 starts running earlier as if the timing to start the operation of the main carrying roll 31 is not T.sub.3 but T.sub.3 ' as a result of adjustment of the above-mentioned read registration in this state, a transfer material delayed to the extent not to be detected by jam detection is fed out from the main carrying roll 31 as the optimum loop quantity cannot be generated between the carrying rolls 31 and 32 since the loop quantity generating time is T.sub.L ' so that there is produced a problem that the transfer material is delayed in the carrying direction to thereby produce such a transfer fault as mentioned above.